The failure of herbicides to control resistant weeds is a problem especially when such weeds are growing in field of herbicide resistant crops that may have lower herbicide resistance than the weed. Herbicide-resistant weeds are identified with a variety of modes of action. Resistance resulting from selection for multiple copies of genes producing herbicide targeted proteins in pigweed is reported by Gaines et al. (2010) Proc. Natl. Acad. Sci. USA, 107(3):1029-1034. Resistance resulting from mutations in genes producing herbicide targeted proteins in goosegrass, prickly lettuce, and ryegrass are reported by Baerson et al. (2002) Plant Physiol., 129(3):1265-1275; Preston et al. (2006) Pesticide Biochem. Physiol., 84(3):227-235; and Wakelin et al. (2006) Weed Res. (Oxford), 46(5):432-440. Vacuolar sequestration of glyphosate is an observed mechanism in glyphosate resistant horseweed; see Ge et al. (2010) Pest Management Sci., 66:576-576. Resistance resulting from expression of enzymes that metabolize herbicides to an inactive chemical form in hairy crabgrass is reported by Hidayat et al. (1997) Pesticide Biochem. Physiol., 57(2):137-146. Reddy et al. (2008) J. Agric. Food Chem., 56(6):2125-2130 reported the accumulation of aminomethylphosphonic acid in plant species treated with glyphosate.